Diesel engines have higher efficiency than gasoline engines due to the increased compression ratio of the diesel combustion process and the higher energy density of diesel fuel. As a result, a diesel engine provides improved gas mileage than an equivalently sized gasoline engine.
The diesel combustion cycle produces particulates that are typically filtered from the exhaust gases. A diesel particulate filter (DPF) is usually disposed along the exhaust stream to filter the diesel particulates from the exhaust. Over time, however, the DPF becomes full and must be regenerated to remove the trapped diesel particulates. During regeneration, the diesel particulates are burned within the DPF to enable the DPF to continue its filtering function.
One traditional regeneration method injects diesel fuel into the cylinder after the main combustion event. The post-combustion injected fuel is expelled from the engine with the exhaust gases and is combusted over catalysts placed in the exhaust stream. The heat released during the fuel combustion on the catalysts increases the exhaust temperature, which burns the trapped soot particles in the DPF. This approach utilizes the common rail fuel injection system and does not require additional fuel injection hardware.
Typically, there is a series of criteria that must be met before regeneration is enabled. One such criteria includes the exhaust temperature achieving a threshold temperature to enable light-off of the post-injected fuel. However, the exhaust temperature achieving a threshold temperature does not accurately indicate whether a hydrocarbon fuel can be combusted within the exhaust under all operating conditions.